The present invention relates to silanes, and more particularly, it relates to novel fluorosilanes used to produce fluorinated silicones and to processes for the preparation of such fluorosilanes.
The elastomers of fluorosilicones, among which the most frequently encountered are the derivatives of poly(trifluoropropylmethylsiloxane) having the structure: ##STR1## are known for their stability over a large temperature range and their excellent resistance to chemical agents, to liquid fuels, to oils, and to solvents. Moreover, with respect to other fluorinated elastomers, these fluorinated silicones retain a good level of properties at extreme temperatures. These properties, and above all the solvent resistance, arise from the carbon-fluorine chemical bond.
There are a number of patents relating to the synthesis of fluorinated silicones or to those fluorosilanes which can be used for their preparation. These fluorosilanes have on a silicon atom at least one group permitting later polycondensation (particularly a chlorine atom or an alkoxy group) and are generally obtained by the hydrosilylation of fluorinated olefins in the presence of a catalyst, usually hexachloroplatinic acid or one of its derivatives, according to the reaction: ##STR2## wherein R.sub.1, R.sub.2, and R.sub.3 represent groups, at least one of which permits later polycondensation to silicone, R.sub.F is a fluorinated chain, and W is a direct linkage or a divalent linkage, for example, by an ether group, an ester group, an amide, a sulfonamide, a urethane, and the like. These can be seen, for example, in British Pat. No. 869,343, and U.S. Pat. Nos. 3,012,006 and 3,422,131. Unfortunately, this hydrosilylation reaction is often difficult to carry out in practice except in the case of allylic derivatives, such as (CF.sub.3).sub.2 --CH--O--CH.sub.2 CH.dbd.CH.sub.2.
U.S. Pat. No. 3,794,672 shows fluorosilanes having the formula: EQU R.sub.A --CH.sub.2 CH.sub.2 --S--R.sub.B --Si
wherein R.sub.A is a perfluoroalkyl radical having from one to four carbon atoms and R.sub.B is an alkylene radical also having one to four carbon atoms. These fluorosilanes are obtained by the radical reaction of an olefin having the formula R.sub.A CH.dbd.CH.sub.2 on a silicon thiol having the formula: EQU HS--R--Si
The Chemical Abstracts 93, 99 (1980), no. 73717u abstract mentions compounds similar to those in U.S. Pat. No. 3,794,672 but obtained by the reaction of a fluorinated thiol and a vinylsilane.